1. Field of the Invention
The invention relates to a method for testing a workpiece using ultrasound. In order to test workpieces in a non-destructive manner using ultrasound, it is known to generate an ultrasound signal by means of an ultrasonic test head, said ultrasound signal being coupled into the workpiece under test either directly via air or by means of a liquid jet, such as a water jet for example, along a prespecified path on the surface of the workpiece. In the case of this so-called squirter technique, a liquid jet is formed by means of a nozzle and is then directed onto the surface of the workpiece. In order to couple-in the ultrasound along the prespecified path, the liquid jet is moved owing to a corresponding movement of the nozzle. The nozzle is moved for this purpose over the stationary workpiece, for example by means of a large mobile portal, synchronized linear shafts or other devices with the same purpose as a test fork, also called yoke.
2. Background and Relevant Art
The test mechanism provides a position for the position of the squirter nozzle. Test mechanisms can be portals with extension arms, linear shaft systems or else robots. The tool center point represents the point at which the jet strikes the component under test. This point is defined by the 3-dimensional position of the squirter nozzle and the distance from the component.
It is also possible for a plurality of squirter nozzles to be used in parallel.
In order to achieve the greatest possible productivity, the acceleration and the final speed of the movement along the path have to be selected to be as high as possible, so that a test period which is as short as possible is achieved. However, the liquid jet is deflected at the same time owing to mass inertia and air resistance. This is all the more severe the higher the acceleration and final speed are selected to be. This deflection has an adverse effect on the test result. In extreme cases, the test becomes unusable if the deflection of the liquid jet becomes too severe.
US 2009/120189 A1, U.S. Pat. No. 3,712,119 A and WO 2012/062343 A1 disclose conventional ultrasound testing methods in which the ultrasound signal is coupled into the workpiece by means of a direct contact or a coupling medium. The workpiece moves in relation to an ultrasonic transducer during the ultrasound testing operation.
U.S. Pat. No. 5,373,743 discloses a method for testing a workpiece, in which an ultrasound signal is coupled into a workpiece by means of a liquid jet. The liquid jet is guided along a path over the surface of the workpiece.